Vehicle Ad-Hoc Networks (VANETS) and similar networks for pedestrians and bicyclists are very different from traditional ad hoc networks. In VANETS, most network nodes are mobile, with a significant fraction of links breaking every second. Most nodes are both data sources (transmitters) and data sinks (receivers) and output data almost continuously. The nodes have information needs that are continuously changing based upon their position. They may be spaced far apart, as when they leave the dense urban cores, and sometimes operate in “urban canyons” with very poor wireless connectivity. Network congestion, link instability and vehicle density vary widely and may change rapidly, as when a traffic light changes, releasing a queue of waiting vehicles. Network congestion, scalability issues, link instability and the complexity of application-building pose problems for these networks that would be nearly insurmountable using current techniques.
Two early large projects on large wireless ad hoc networks are CarNet and Fleetnet, discussed by R. Meier and V. Cahill, see “Exploiting proximity in event-based middleware for collaborative mobile applications,” in Proc. Distributed Applications and Interoperable Systems: 4th IFIP WG6.1 International Conference, pages 285-296, 2003; and by H. Hartenstein et al., see “Position-aware ad hoc wireless networks for inter-vehicle communications: The fleetnet project,” in Proc. ACM Symposium on Mobile ad hoc networking and computing, pages 259-262, 2001.
Routing protocols for VANETs have been disclosed, for example, by R. Morris et al., see “Carnet: a scalable ad hoc wireless network system,” in Proc. 9th workshop on ACM SIGOPS European Workshop, pages 61-65, 2000; Hartenstein et al. (previously cited); L. Wischhof et al., see “Adaptive broadcast for travel and traffic information distribution based on intervehicle communication,” in Proc. Intelligent Vehicle Symposium, IEEE, 2003; and by J. Tian et al., see “Spatially aware packet routing for mobile ad hoc intervehicle radio networks,” in Proc. ITSC. IEEE, 2003.
Security issues in VANETs have been disclosed, for example, by J. Hubaux et al., see “The security and privacy of smart vehicles,” in Security and Privacy Magazine, volume 2(3); M. E. Zarki et al., see “Security issues in a future vehicular network,” in European Wireless, 2002; P. Golle et al., see “Detecting and correcting malicious data in VANETs,” in Proc. ACM VANET '04, 2004; and control issues are discussed by M. T. J. Hedrick et al., see “Control issues in automated highway systems,” in IEEE Control Systems Magazine, volume 14(6), pages 21-32, 1994.
VANET safety applications have been disclosed, for example, L. Briesemeister et al., see “Disseminating messages among highly mobile hosts based on inter-vehicle communications,” in Proc. IEEE Intelligent Vehicles Symposium, October 2000; J. Yin, et al., see “Performance evaluation of safety applications over DSRC vehicular ad hoc networks,” in Proc. ACM VANET '04, October 2004; Route planning and transportation are discussed by J. Wahle, see “Information in intelligent transportation systems,” in Ph.D. Thesis, January 2002.
The issue of proximity based data dissemination has been discussed (by R. Meier and V. Cahill, see “Exploiting proximity in event-based middleware for collaborative mobile applications,” in Proc. Distributed Applications and Interoperable Systems: 4th IFIP WG6.1 International Conference, pages 285-296, 2003), teaching an architecture that allows proximity based subscription to information based on proximity where different applications can subscribe to information within different distances. However, the possibility of a fractional amount of information reaching a destination is not disclosed.
The idea of layered data dissemination is discussed by L. B. Michael (see “Adaptive layered data structure for inter-vehicle communication in ad hoc communication networks,” in Proc. 8th World Congress on Intelligent Transportation, 2001) that was motivated by a proximity-based need for information in different applications. Using Michael's data structure, packets are transmitted with layers of data which are successively removed from the data structure as the information travels further from the source. A disadvantage to this approach is that it prohibits the possibility of fractional information of any form different from that present in the layered data structure. Moreover, neither Meier and Cahill nor Michael quantifies the need for variable resolution information based on proximity to the source of the information.